175TS with 125S engine project

[George]

At long last I have fitted new rectifier as recommended by Max (veloduke). Pleased to say bike started 3rd kick after three weeks in cold shed.
I have taken some voltage readings across battery and would appreciate any comments whether readings are as they should be and if there are any other tests I should make. Not able to takes bike for a long ride yet what with lockdown.
Battery disconnected 6.3 Volts fully charged
Ignition on, engine off, lights off 6.25 Volts
Ignition on, engine off. headlight on 5.95 Volts

Ignition on, engine fast tickover lights off 6.46 Volts
Ignition on, engine fast tickover headlight on 6 Volts

Ignition on, engine high revs, lights off 7.5 Volts
Ignition on, engine high revs, headlight on 6.23 Volts
I wonder if I swopped the two yellow wires that should be one yellow one white if I might get a higher charge rate at high revs and lights on. Will swop wires and test again.

With headlight on light gets brighter from tickover to high revs.

Of course I will have to have a 10 mile ride out to check if battery is gassing or if problem solved. Fingers crossed.

[Ventodue]

All that seems fine, George.

The 'gassing' charge for a 6 volt battery is around 7.05v (the exact value depends on the ambient temperature, the state of the battery before charging and whether the Moon is aligned with Mars on that particular day ...), so you should be ok.

Your 'headlights on' charge voltage of 6.23 volts is pretty impressive, in fact. It means there is virtually no nett loss of power. A battery cell starts recharging at around 2.15v, i.e. 6.45v for a 3 cell, nominal 6 volt battery. You'll struggle to do better IMO.

Bravo!

Craig

[veloduke]

Hi George

Your figures below, mine in red in brackets;

Battery disconnected 6.3 Volts fully charged (6.5)
Ignition on, engine off, lights off 6.25 Volts (6.4)
Ignition on, engine off. headlight on 5.95 Volts (5.9)

Ignition on, engine fast tickover lights off 6.46 Volts (6.7)
Ignition on, engine fast tickover headlight on 6 Volts (6.0)

Ignition on, engine high revs, lights off 7.5 Volts (7.5)
Ignition on, engine high revs, headlight on 6.23 Volts (6.2)

Very similar.

Also, our ideas of fast tickover are likely different, where the voltage was measured (battery terminal and cylinder fin for me), and differences between the meters.

Reading the (Italian) manual, it's as if they expected the battery to discharge with the lights on, a reason for having such a large battery perhaps?

I mean, if it's a 40W alternator - 25W for the headlight, 5W for the taillight, 10W+ for the ignition, then load is greater than generation capacity.

I think your system's OK.

[George]

Thanks for the prompt reply Max. That is an encouraging set of comparison readings.
You may recall that I had two yellow wires from stator one of which should be white and no way of finding the correct white wire. Out of curiosity I will reverse the wires at terminal block and take another set of readings. Will post figures when finished, might help anyone else with same problem

[veloduke]

That will be interesting.

I also did the check from the manual regarding measuring the current between the windings.
Not strictly accurate as I didn't isolate the windings (so the ignition circuit was still connected) but here goes anyway;

Ammeter between white and yellow - manual says 6.5 to 7 amps - I measured 5.6 amps
Ammeter between white and red - manual says 2 amps (4 for 125S) - I measured 2.75 amps

So that's about an amp difference for both readings, probably owing to the alternator being still in circuit.
Good enough for me.

[Ventodue]

<snip> Reading the (Italian) manual, it's as if they expected the battery to discharge with the lights on ...

Yup, you got it

[George]

I have reversed the two yellow wires and my new readings are in green

My figures below, veloduke figures in red in brackets;

Battery disconnected 6.3 Volts fully charged (6.5) 6.28
Ignition on, engine off, lights off 6.25 Volts (6.4) 6.06
Ignition on, engine off. headlight on 5.95 Volts (5.9) 5.84

Ignition on, engine fast tickover lights off 6.46 Volts (6.7) 7.4 6.5 with slow tickover
Ignition on, engine fast tickover headlight on 6 Volts (6.0) 6.2 6.0 with slow tickover

Ignition on, engine high revs, lights off 7.5 Volts (7.5) 7.3
Ignition on, engine high revs, headlight on 6.23 Volts (6.2) 6.2

Not a lot of difference apart from fast tickover lights off 7.4 and high revs lights off 7.3 making them more consistent and less chance of battery gassing off. When I had wires other way round high revs lights off gave 7.5 increasing to 7.6 (did not over rev my new engine) I was given to believe that 7.5 was when battery would gas off, as mentioned by Craig in earlier post.
My multimeter reads DC current only and not AC current. I am unable to check output of windings red to white and red to yellow

I think I will leave wires this way round and have a good test ride when I can.
This agrees with my earlier post:
"Looking at excellent wiring diagram supplied by Jon, it would seem that white wire is connected part way along top coil and my reasoning is that this should have a lower resistance than yellow to red. My readings are: Yellow 1 to red = 0.5 ohms. Yellow 2 to red = 0.7 ohms. If my theory is correct, this would indicate that yellow 1 is the white connection"

Thanks for all the input so far.

[Ventodue]

Give it go, George. I could be concerned that, with the headlight off, you're pumping nearly 7.5 volts into a fully charged battery. But then again, for a regular lead acid battery, Battery University reckons:

"At 20°C (68°F), gassing starts at a charge voltage of 2.415v/cell. At –20°C (0°F), the gassing threshold rises to 2.97v/cell"*

... which for your 6 volt battery equates to a range of 7.2 - 8.91 volts.

So if in doubt, either put the light on. Or only ride when it's cold outside ...

Do let us know how it turns out.


* https://batteryuniversity.com/learn/art ... mperatures

[George]

Give it go, George. I could be concerned that, with the headlight off, you're pumping nearly 7.5 volts into a fully charged battery. But then again, for a regular lead acid battery, Battery University reckons:

"At 20°C (68°F), gassing starts at a charge voltage of 2.415v/cell. At –20°C (0°F), the gassing threshold rises to 2.97v/cell"*

... which for your 6 volt battery equates to a range of 7.2 - 8.91 volts.

So if in doubt, either put the light on. Or only ride when it's cold outside ...

Do let us know how it turns out.


* https://batteryuniversity.com/learn/art ... mperatures

That's a good observation with the 7.4 v at tickover, could be indicating that I have the higher output coil connected to lights off position. As my first set of readings were almost the same as veloduke's bike readings and he has had no problems I am going to change back to first way round. and give it a go

[George]

Checked my readings again. Lights off.
Tickover 6.5V fast tickover 7.4V high revs 7.65V and rising

Changed two yellow wires (one is white!) back to first setting checked readings again
Tickover 6.3V Fast tickover 6.5V high revs 7.5V
This setting makes more sense and once again thanks Craig (ventodue) for pointing out high charge at low revs.
Taking this as correct and will leave for road test.